Glycation, carbonyl stress, EAGLEs, and the vascular complications of diabetes

The association between poor metabolic control and the microvascular complications of diabetes is now well established, but the relationship between long-term metabolic control and the accelerated atherosclerosis of diabetes is as yet poorly defined. Hyperglycemia is the standard benchmark by which metabolic control is assessed. One mechanism by which elevated glucose levels may mediate vascular injury is through early and advanced glycation reactions affecting a wide variety of target molecules. The "glycation hypothesis'' has developed over the past 30 years, evolving gradually into a "carbonyl stress hypothesis'' and taking into account not only the modification of proteins by glucose, but also the roles of oxidative stress, a wide range of reactive carbonyl-containing intermediates (derived not only from glucose but also from lipids), and a variety of extra- and intracellular target molecules. The final products of these reactions may now be termed "Either Advanced Glycation or Lipoxidation End-Products'' or "EAGLEs.'' The ubiquity of carbonyl stress within the body, the complexity of the reactions involved, the variety of potential carbonyl intermediates and target molecules and their differing half-lives, and the slow development of the complications of diabetes all pose major challenges in dissecting the significance of these processes. The extent of the reactions tends to correlate with overall metabolic control, creating pitfalls in the interpretation of associative data. Many animal and cell culture studies, while supporting the hypothesis, must be viewed with caution in terms of relevance to human diabetes. In this article, the development of the carbonyl stress hypothesis is reviewed, and implications for present and future treatments to prevent complications are discussed.

Glycation does not alter LDL-induced secretion of tissue plasminogen activator and plasminogen activator inhibitor-1 from human aortic endothelial cells

Diabetes may induce both quantitative and qualitative changes in lipoproteins, especially low-density lipoprotein (LDL). Effects of LDL glycation on endothelial cell secretion of tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) have not been fully elucidated. Human aortic endothelial cell (HAEC) tPA and PAI-1 production were determined after incubation with LDL (50 to 500 microg/mL protein, 24 h) from three sources: (1) nondiabetic LDL (N-LDL) modified in vitro to form six preparations: native, nonmodified (N); glycated (G); minimally oxidized (MO); minimally oxidized and glycated (MOG); heavily oxidized (HO); and heavily oxidized and glycated (HOG); (2) in vivo glycated and relatively nonglycated LDL subfractions from type 1 diabetic patients; (3) LDL from type 1 diabetic patients and matched controls, which was subfractionated using density gradient ultracentrifugation. In experiments using LDL modified in vitro, the rate of tPA release by HAECs incubated with N-LDL (83 +/- 4 ng/mg cell protein/24 h) did not differ significantly from those incubated with G-LDL (73 +/- 7), MO-LDL (74 +/- 13), or MOG-LDL (66 +/- 15) and was not influenced by LDL concentration. The rate of PAI-1 release was similar in HAECs incubated with N-LDL (5.7 +/- 0.6 mug/mg cell protein/24 h), G-LDL (5.7 +/- 0.7), MO-LDL (5.5 +/- 0.8), or MOG-LDL (5.7 +/- 0.9) and was not influenced by LDL concentration. In contrast, tPA release was significantly decreased in cells incubated with LDL (10 microg/mL) modified extensively by oxidation, and averaged 45.2 +/- 5.0 and 43.7 +/- 9.9 ng/mg/24 h for HO-LDL and HOG-LDL, respectively, and was further decreased with increasing concentrations of the heavily oxidized LDL preparations. PAI-1 release was not significantly decreased relative to N-LDL in cells incubated with low concentrations (5 to 50 microg/mL) of HO-LDL and HOG-LDL, but was decreased to 3.2 +/- 0.5 and 3.1 +/- 0.7 microg/mg/24 h for HO-LDL and HOG-LDL at 200 microg/mL, respectively. Results using in vivo glycated versus nonglycated LDL showed that tPA and PAI-1 release did not differ between subfractions. Release of tPA averaged 5.11 +/- 0.6 and 5.12 +/- 0.7 ng/mg/24 h, whereas release of PAI-1 averaged 666 +/- 27 ng/mg/24 h and 705 +/- 30 ng/mg/24 h for nonglycated and glycated LDL subfractions, respectively. Using LDL of different density subclasses, tPA and PAI-1 release in response to LDL from diabetic patients compared with control subjects did not differ when HAECs were incubated with LDLs of increasing density isolated from each subject pair. We conclude that oxidation of LDL, but not glycation, may contribute to the altered fibrinolysis observed in diabetes.

Effects of modified low-density lipoproteins on human retinal pericyte survival

According to a current paradigm cardiovascular diseases can be initiated by exposure of vascular cells to qualitatively modified low-density lipoproteins (LDL). Capillary leakage, an early feature of diabetic retinopathy, results in the exposure of retinal pericytes to modified LDL, including glycated (G-LDL) and heavily oxidized glycated LDL (HOG-LDL). We demonstrate here that modified LDL inhibits the proliferation and survival of cultured human retinal pericytes. Modified LDL also induced DNA fragmentation in bovine retinal pericytes. Overall, HOG-LDL produced a significantly higher extent of cytotoxicity and apoptosis in retinal pericytes. These results indicate that exposure of pericytes to HOG-LDL could be implicated in the development of diabetic retinopathy.

Effects of oxidized and glycated LDL on gene expression in human retinal capillary pericytes

PURPOSE

Modified (oxidized and/or glycated) low-density lipoproteins (LDLs) have been implicated in retinal pericyte loss, one of the major pathologic features of early-stage diabetic retinopathy. To delineate underlying molecular mechanisms, the present study was designed to explore the global effects of modified LDL on pericyte gene expression.

METHODS

Quiescent human retinal pericytes were exposed to native LDL (N-LDL), glycated LDL (G-LDL), and heavily oxidized-glycated LDL (HOG-LDL) for 24 hours, and gene expression was evaluated by DNA microarray analysis. Several of the gene responses were checked, and in each case confirmed by reverse-transcription real-time PCR.

RESULTS

HOG-LDL induced a gene expression pattern markedly distinct from that of N-LDL or G-LDL, whereas G-LDL elicited gene expression similar to that of N-LDL. A comparison of responses to HOG-LDL versus N-LDL revealed 60 genes with expression that varied by > or =1.7-fold. The HOG-LDL-responsive genes included members of functional pathways, such as fatty acid, eicosanoid, and cholesterol metabolism; fibrinolytic regulation; cell growth and proliferation; cell stress responses; the kinin system; and angiogenesis.

CONCLUSIONS

HOG-LDL elicits gene expression in retinal pericytes that may contribute to pericyte loss and other retinal abnormalities in diabetic retinopathy. Observed proapoptotic and proangiogenic responses to HOG-LDL may be of particular importance in this regard. The genes identified through these studies provide potential therapeutic targets for the prevention and treatment of diabetic retinopathy.

Effect of intensive glycemic control on levels of markers of inflammation in type 1 diabetes mellitus in the diabetes control and complications trial

BACKGROUND

Type 1 diabetes mellitus is associated with an increased risk of cardiovascular disease (CVD) that is not fully explained by conventional risk factors. The Diabetes Control and Complications Trial (DCCT) showed that intensive diabetes therapy reduced levels of LDL cholesterol and triglycerides but increased the risk of major weight gain, which might adversely affect CVD risk. The present study examined the effect of intensive therapy on levels of several markers of inflammation that have been linked to risk of CVD.

METHODS AND RESULTS

We measured levels of inflammatory biomarkers in stored baseline and 3-year follow-up serum specimens from a random sample of 385 participants in the DCCT, a multicenter trial in which 1441 subjects aged 13 to 39 years with type 1 diabetes mellitus were randomized to intensive or conventional diabetes treatment. The markers included high-sensitivity C-reactive protein (hsCRP), soluble intercellular adhesion molecule type 1 (sICAM-1), soluble vascular cell adhesion molecule type 1 (sVCAM-1), and the 55-kDa soluble tumor necrosis factor-alpha receptor 1 (sTNF-R1). We examined the effect of intensive therapy on the change in levels of the inflammatory markers. In unadjusted analyses, levels of hsCRP and sTNF-R1 increased in both treatment groups after 3 years of follow-up, with no significant difference between groups for hsCRP (P=0.53) but with a greater increase of sTNF-R1 in the intensive therapy group (P=0.002). In contrast, mean levels of sICAM-1 and sVCAM-1 decreased among participants assigned to intensive therapy, whereas they did not change among those in the conventional treatment group (P=0.03 for sICAM-1; P=0.03 for sVCAM-1). After adjustment for baseline levels and other factors, intensive therapy remained associated with a significant decrease in sICAM-1 (P=0.02) and an increase in sTNF-R1 (P=0.03). For hsCRP, there was a significant interaction between the top third of weight gain and treatment assignment (P=0.03). In subgroup analyses among subjects undergoing intensive therapy, hsCRP levels increased among those who gained the most weight, whereas it decreased among those in the bottom third of weight gain (P=0.0004).

CONCLUSIONS

Intensive therapy in patients with type 1 diabetes mellitus reduced levels of sICAM-1 and increased levels of sTNF-R1 and of hsCRP among those who gained weight. These data demonstrate that the effect of intensive therapy on inflammation is complex and, to the extent that hsCRP is a risk factor, suggest that the risk of atherosclerosis among diabetic patients may be influenced by the degree of weight gain while undergoing intensive therapy.

The tidemark of the chondro-osseous junction of the normal human knee joint

The chondro-osseous junction includes the junction between calcified and non-calcified cartilage matrices often referred to as the tidemark. A detailed knowledge of the structure, function and pathophysiology of the chondro-osseous junction is essential for an understanding both of the normal elongation of bones and of the pathogenesis of osteoarthrosis. In this study the molecular anatomy of the tidemark was studied using histochemical techniques, including lectin histochemistry, on blocks of normal cartilage from human knee joints. The tidemark stained with H and E, picro-sirius red, toluidine blue, safranin O and methyl green, but not with alcian blue in the presence of magnesium chloride at 0.05 M or above. It stained with only four lectins, those from Datura stramonium, Maclura pomifera, Erythrina crystagalli and Helix pomatia, out of the 19 used. Therefore, it is rich in collagen and contains hyaluronan, but appears to lack the glycosaminoglycans of 'conventional' proteoglycans and it expresses a very limited and distinctive lectin staining glycoprofile, which is probably attributable to specific glycoproteins. In addition, the tidemark had a distinct microanatomical trilaminate appearance. From all of these results it is clear that this part of the chondro-osseous junctional region is chemically more complex and distinctive than has previously been described.

Apolipoprotein C-III protein concentrations and gene polymorphisms in Type 1 diabetes: associations with microvascular disease complications in the DCCT/EDIC cohort

AIM

We investigated the associations of apolipoprotein C-III (apoCIII) protein and apoCIII gene variation with microvascular disease complications in Type 1 diabetes.

METHODS

The serum apoCIII concentration, and both a T(-455)-->C and a SacI gene polymorphisms were determined in 409 patients in the DCCT/EDIC cohort of patients with Type 1 diabetes. Correlations with albumin excretion rate (AER) and the severity of retinopathy were investigated.

RESULTS

Higher apoCIII concentrations were associated (P<.0001) with increased triglycerides (r=.78), total (r=.61) and LDL (r=.40) cholesterol, apoAI (r=.26), and apoB (r=.50), AER (r=.08), and the severity of retinopathy (ETDRS score, r=.11), and these relationships persisted after controlling for age, gender, body mass index (BMI), and HbA1c level. The apoCIII concentration was significantly higher in the group of patients with macroalbuminuria (AERs 300 mg/24 h) compared to the groups with microalbuminuria (AER 40-299 mg/24 h; P<.0001) or normoalbuminuria (AER <40 mg/24 h) (P<.0001). The apoCIII concentration also was significantly higher in the group of patients with severe retinopathy (ETDRS 10-23) compared to those with moderate (ETDRS 4-9; P<.02) or mild retinopathy (ETDRS 1-3; P<.0001). Neither the T(-455)-->C polymorphism nor a SacI polymorphism in the 3' UTR were associated with circulating apoCIII concentrations, nor the severity of nephropathy or retinopathy.

CONCLUSIONS

Elevated apoCIII levels have been associated with increased macrovascular disease risk. In the DCCT/EDIC cohort of patients, there was an independent positive association of apoCIII level with microvascular complications of Type 1 diabetes.

Lipoproteins and diabetic microvascular complications

Risk factors for the microvascular complications (nephropathy and retinopathy) of Type 1 and Type 2 diabetes mellitus and the associated accelerated atherosclerosis include: age, diabetes duration, genetic factors, hyperglycaemia, hypertension, smoking, inflammation, glycation and oxidative stress and dyslipoproteinaemia. Hypertriglyceridaemia, low HDL and small dense LDL are common features of Type 2 diabetes and Type 1 diabetes with poor glycaemic control or renal complications. With the expansion of knowledge and of clinical and research laboratory tools, a broader definition of 'lipid' abnormalities in diabetes is appropriate. Dyslipoproteinaemia encompasses alterations in lipid levels, lipoprotein subclass distribution, composition (including modifications such as non-enzymatic glycation and oxidative damage), lipoprotein-related enzymes, and receptor interactions and subsequent cell signaling. Alterations occur in all lipoprotein classes; chylomicrons, VLDL, LDL, HDL, and Lp(a). There is also emerging evidence implicating lipoprotein related genotypes in the development of diabetic nephropathy and retinopathy. Lipoprotein related mechanisms associated with damage to the cardiovascular system may also be relevant to damage to the renal and ocular microvasculature. Adverse tissue effects are mediated by both alterations in lipoprotein function and adverse cellular responses. Recognition and treatment of lipoprotein-related risk factors, supported by an increasing array of assays and therapeutic agents, may facilitate early recognition and treatment of high complication risk diabetic patients. Further clinical and basic research, including intervention trials, is warranted to guide clinical practice. Optimal lipoprotein management, as part of a multi-faceted approach to diabetes care, may reduce the excessive personal and economic burden of microvascular complications and the related accelerated atherosclerosis.

Apolipoprotein C-III protein concentrations and gene polymorphisms in type 1 diabetes: associations with lipoprotein subclasses

Serum apolipoprotein C-III (apoCIII) concentration and apoCIII gene polymorphisms have been shown to be a risk factor for cardiovascular disease; however, the underlying mechanisms remain unclear. In addition, no studies have been performed that address these issues in type 1 diabetes. The current study investigated apoCIII protein and apoCIII gene variation in a normotriglyceridemic (82 +/- 57 mg/dL) population of patients with type 1 diabetes, the Diabetes Control and Complications Trial/Epidemiology of Diabetes Intervention and Complications (DCCT/EDIC) cohort. Blood samples were obtained in 409 patients after an overnight fast. Serum apoCIII concentration was highly correlated with multiple changes in lipids and lipoproteins that resulted in an adverse cardiovascular disease risk profile. Higher apoCIII concentrations were associated (P < .0001) with increased triglycerides (r = 0.78), total (r = 0.61) and low-density lipoprotein (LDL) (r = 0.40) cholesterol, apoA-I (r = 0.26), and apoB (r = 0.50), and these relationships persisted after controlling for age, gender, body mass index (BMI), and hemoglobin A1c (HbA1c). Nuclear magnetic resonance (NMR) lipoprotein subclass analyses demonstrated that apoCIII was correlated with an increase in very-low-density lipoprotein (VLDL) subclasses (P = .0001). There also was a highly significant positive relationship between serum apoCIII concentration and the LDL particle concentration in both men (r = 0.49, P = .001) and women (r = 0.40, P = .001), and a highly significant negative relationship between serum apoCIII levels and average LDL particle size in both men (r = -0.37, P = .001) and women (r = -0.22, P = .001) due primarily to an augmentation in the small L1 subclass (r = 0.42, P = .0001). Neither the T(-455) --> C polymorphism affecting an insulin response element in the apoCIII gene promoter nor a SacI polymorphism in the 3'UTR were associated with any alterations in circulating apoCIII concentrations, serum lipids, apolipoprotein concentrations, lipoprotein composition, or parameters measured by NMR lipoprotein subclass analyses. In summary, elevated apoCIII concentration was associated with risk factors for cardiovascular disease in normolipidemic type 1 diabetic patients through associated changes in lipoprotein subfraction distributions, which were independent of apoCIII genotype.

'Lipoproteins, glycoxidation and diabetic angiopathy'

The chronic vascular complications of diabetes (nephropathy, retinopathy and accelerated atherosclerosis) are a major cause of morbidity and premature mortality. In spite of the more widespread availability of intensive diabetes management, approximately one in three people with diabetes develop aggressive complications and over 70% die of atherosclerosis-related diseases. Genetic and acquired factors are likely to be contributory. Potential mediators of vascular damage may include the interrelated processes of lipoprotein abnormalities, glycation, oxidation and endothelial dysfunction. Lipoprotein abnormalities encompass alterations in lipid concentrations, lipoprotein composition and subclass distribution and lipoprotein-related enzymes. Nonenzymatic glycation and oxidative damage to lipoproteins, other proteins and to vascular structures may also be deleterious. As atherosclerosis is a chronic condition commencing in youth, and because clinical events may be silent in diabetes, surrogate measures of vascular disease are important for early identification of diabetic patients with or at high risk of vascular damage, and for monitoring efficacy of interventions. The increasing array of biochemical assays for markers and mediators of vascular damage, noninvasive measures of vascular health, and therapeutic options should enable a reduction in the excessive personal and economic burden of vascular disease in type 1 and type 2 diabetes.

In vivo glycated low-density lipoprotein is not more susceptible to oxidation than nonglycated low-density lipoprotein in type 1 diabetes

It has been suggested that low-density lipoprotein (LDL) modified by glycation may be more susceptible to oxidation and thus, enhance its atherogenicity. Using affinity chromatography, LDL glycated in vivo (G-LDL) and relatively nonglycated. (N-LDL) subfractions can be isolated from the same individual. The extent of and susceptibility to oxidation of N-LDL compared with G-LDL was determined in 15 type 1 diabetic patients. Total LDL was isolated and separated by boronate affinity chromatography into relatively glycated (G-) and nonglycated (N-) subfractions. The extent of glycation, glycoxidation, and lipoxidation, lipid soluble antioxidant content, susceptibility to in vitro oxidation, and nuclear magnetic resonance (NMR)-determined particle size and subclass distribution were determined for each subfraction. Glycation, (fructose-lysine) was higher in G-LDL versus N-LDL, (0.28 +/- 0.08 v 0.13 +/- 0.04 mmol/mol lysine, P < .0001). However, levels of glycoxidation/lipoxidation products and of antioxidants were similar or lower in G-LDL compared with N-LDL and were inversely correlated with fructose-lysine (FL) concentrations in G-LDL, but positively correlated in N-LDL. In vitro LDL (CuCl2) oxidation demonstrated a longer lag time for oxidation of G-LDL than N-LDL (50 +/- 0.16 v 37 +/- 0.15 min, P < .01), but there was no difference in the rate or extent of lipid oxidation, nor in any aspect of protein oxidation. Mean LDL particle size and subclass distribution did not differ between G-LDL and N-LDL. Thus, G-LDL from well-controlled type 1 diabetic patients is not more modified by oxidation, more susceptible to oxidation, or smaller than relatively N-LDL, suggesting alternative factors may contribute to the atherogenicity of LDL from type 1 diabetic patients.

Diabetic retinopathy and serum lipoprotein subclasses in the DCCT/EDIC cohort

PURPOSE

To determine associations between retinopathy status and detailed serum lipoprotein subclass profiles in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study (DCCT/EDIC) cohort.

METHODS

Persons with type 1 diabetes (440 women, 548 men) from the DCCT/EDIC cohort were studied. Retinopathy was characterized by Early Treatment Diabetic Retinopathy Study (ETDRS) scores, hard exudate scores, and ETDRS scores minus the hard exudate component. Lipoproteins were characterized by conventional lipid profile, nuclear magnetic resonance lipoprotein subclass profile (NMR-LSP), apoA1, apoB, lipoprotein(a), and susceptibility of LDL to oxidation. Data were analyzed with and without the following covariates: age, gender, duration of diabetes, HbA(1c), albumin excretion rate (AER), creatinine clearance, hypertension, body mass index, waist-hip ratio, DCCT treatment group, smoking status.

RESULTS

The severity of retinopathy was positively associated with triglycerides (combined cohort) and negatively associated with HDL cholesterol (men, combined cohort). NMR-LSP identified retinopathy as being positively associated with small and medium VLDL and negatively with VLDL size. In men only, retinopathy was positively associated with small LDL, LDL particle concentration, apoB concentration, and small HDL and was negatively associated with large LDL, LDL size, large HDL, and HDL size. No associations were found with apoA1, Lp(a), or susceptibility of LDL to oxidation. All three measures of retinopathy revealed the same associations.

CONCLUSIONS

NMR-LSP reveals new associations between serum lipoproteins and severity of retinopathy in type 1 diabetes. The data are consistent with a role for dyslipoproteinemia involving lipoprotein subclasses in the pathogenesis of diabetic retinopathy.

Nephropathy in a Hypercholesterolemic Mouse Model with Streptozotocin-Induced Diabetes

BACKGROUND/AIMS

The contribution of preexisting hypercholesterolemia to diabetic nephropathy remains unclear. We assessed the impact of hypercholesterolemia on diabetic nephropathy using a double knockout (DKO) mouse, null for the low-density lipoprotein receptor (LDLRNDASH;/NDASH;) and the apoB mRNA editing catalytic polypeptide 1 (APOBEC1NDASH;/NDASH;).

METHODS

Wild-type (WT) and DKO mice received sham or streptozotocin injections at age 7 weeks, yielding control (WT-C, DKO-C) and diabetic (WT-D, DKO-D) groups. At sacrifice (age 40 weeks), albuminuria was determined by ELISA, and kidney sections were examined by light and electron microscopy.

RESULTS

Albuminuria increased in diabetic mice (WT-D: 82.4 +/- 37.2 microg/18 h; DKO-D: 58.0 +/- 45.7 microg/18 h) versusnondiabetic controls (WT-C: 10.2 +/- 7.2 microg/18 h; DKO-C: 8.6 +/- 5.3 microg/18 h) (p LT; 0.0001), but was unaffected by hypercholesterolemia. Light microscopy of kidney sections demonstrated increased collagen levels in glomeruli in WT-D mice, but not in DKO-D mice or either control group. Electron microscopy showed a thickened glomerular basement membrane in WT-D mice only. The proximal tubular basement membrane thickness was increased in both diabetic groups versusnondiabetic controls (p LT; 0.01); in WT-D mice this was attributable to collagen accumulation, but in DKO-D mice it was mainly caused by lipid vacuoles.

CONCLUSIONS

In this animal model, preexisting hypercholesterolemia did not exacerbate either glomerular lesions of diabetes (collagen accumulation, basement membrane thickening) or albuminuria, but appeared to mitigate these effects. Furthermore, the combination of hypercholesterolemia and diabetes resulted in a significant lipid accumulation in the tubular basement membrane.

Lipoproteins in the DCCT/EDIC cohort: associations with diabetic nephropathy

BACKGROUND

Lipoproteins may contribute to diabetic nephropathy. Nuclear magnetic resonance (NMR) can quantify subclasses and mean particle size of very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL), and LDL particle concentration. The relationship between detailed lipoprotein analyses and diabetic nephropathy is of interest.

METHODS

In a cross-sectional study, lipoproteins from 428 women and 540 men from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) cohort were characterized by conventional lipid enzymology, NMR, apolipoprotein levels, and LDL oxidizibility. Linear regression was performed for each lipoprotein parameter versus log albumin excretion rate (AER), with and without covariates for age, diabetes duration, HbA1c, hypertension, body mass index, waist-hip ratio, and DCCT treatment group. Significance was taken at P < 0.05.

RESULTS

By multivariate analysis, conventional profile, total triglycerides, total- and LDL cholesterol, but not HDL cholesterol, were associated with AER. NMR-determined large, medium, and small VLDL were associated with AER in both genders (except large VLDL in women), and intermediate density lipoprotein (IDL) was associated with AER (men only). LDL particle concentration and ApoB were positively associated with AER (in men and in the total cohort), and there was a borderline inverse association between LDL diameter and AER in men. Small HDL was positively associated with AER and a borderline negative association was found for large HDL. No associations were found with ApoA1, Lp(a), or LDL oxidizibility.

CONCLUSION

Potentially atherogenic lipoprotein profiles are associated with renal dysfunction in type 1 diabetes and further details are gained from NMR analysis. Longitudinal studies are needed to determine if dyslipoproteinemia can predict patients at risk of nephropathy, or if lipoprotein-related interventions retard nephropathy.

Lipoprotein subclass profiles of hyperlipidemic diabetic mice measured by nuclear magnetic resonance spectroscopy

Dyslipidemia accelerates vascular complications of diabetes. Nuclear magnetic resonance (NMR) analysis of lipoprotein subclasses is used to evaluate a mouse model of human familial hypercholesterolemia +/- streptozotocin (STZ)-induced diabetes. A double knockout (DKO) mouse (low-density lipoprotein receptor [LDLr] -/-; apolipoprotein B [apoB] mRNA editing catalytic polypeptide-1 [Apobec1] -/-) was studied. Wild-type (WT) and DKO mice received sham or STZ injections at age 7 weeks, yielding control (WT-C, DKO-C) and diabetic (WT-D, DKO-D) groups. Fasting serum was collected when the mice were killed (age 40 weeks) for Cholestech analysis (Cholestech Corp, Hayward, CA) and NMR lipoprotein subclass profile. By Cholestech, fasting triglyceride and total cholesterol increased in DKO-C versus WT-C. Diabetes further increased total cholesterol in DKO. High-density lipoprotein cholesterol (HDL-C) was similar among all groups. NMR revealed that LDL in all groups was present in a subclass the size of large human LDL and was increased 48-fold in DKO-C versus WT-C animals, but was unaffected by diabetes. HDL was found in a subclass equivalent to large human HDL, and was similar among groups. In conclusion, NMR analysis reveals lipoprotein subclass distributions and the effects of genetic modification and diabetes in mice, but lack of particles the size of human small LDL and small HDL may limit the relevance of the present animal model to human disease.

Serum lipoproteins in the diabetes control and complications trial/epidemiology of diabetes intervention and complications cohort: associations with gender and glycemia

OBJECTIVE

To relate the nuclear magnetic resonance (NMR)-determined lipoprotein profile, conventional lipid and apolipoprotein measures, and in vitro oxidizibility of LDL with gender and glycemia in type 1 diabetes.

RESEARCH DESIGN AND METHODS

In the 1997-1999 Diabetes Control and Complications Trial/Epidemiology of Diabetes Intervention and Complications (DCCT/EDIC) cohort, serum from 428 women and 540 men were characterized by conventional lipids, NMR, apolipoprotein levels, and LDL susceptibility to in vitro oxidation. Simple and partial correlation coefficients were calculated for each lipoprotein-related parameter versus gender, with and without covariates (age, diabetes duration, concurrent HbA(1c), DCCT randomization, hypertension, BMI, waist-to-hip ratio, and albuminuria). For concurrent HbA(1c), data were analyzed as above, exchanging gender for HbA(1c). Associations were significant if P < 0.05.

RESULTS

Although men and women had similar total and LDL cholesterol and triglycerides, men exhibited the following significant percent differences in NMR profiles versus women: small VLDL 41; IDL -30; medium LDL 39; small LDL 21; large HDL -32; small HDL 35; LDL particle concentration 4; VLDL and HDL diameters -8 and -4, respectively. Small VLDL, small HDL, medium LDL (women only), small LDL (men only), and LDL particle concentration were positively correlated, and HDL size was inversely correlated, with concurrent HbA(1c). NMR profile was unrelated to prior DCCT randomization. Susceptibility of LDL to oxidation was unrelated to gender and glycemia.

CONCLUSIONS

Male gender and poor glycemia are associated with a potentially more atherogenic NMR lipoprotein profile. Neither gender nor glycemia influence LDL oxidation in vitro.

Isotope dilution gas chromatography/mass spectrometry method for the determination of methionine sulfoxide in protein

We have developed a new technique for quantifying methionine sulfoxide (MetSO) in protein to assess levels of oxidative stress in physiological systems. In this procedure, samples are hydrolyzed with methanesulfonic acid (MSA) in order to avoid the conversion of MetSO to methionine (Met) that occurs during hydrolysis of protein in HCl. The hydrolysate is fractionated on a cation exchange column to remove the nonvolatile MSA from amino acids, and the amino acids are then derivatized as their trimethylsilyl esters for analysis by selected ion monitoring-gas chromatography/mass spectrometry. The limit of detection of the assay is 200 pmol of MetSO per analysis, and the interassay coefficient of variation is 5.8%. Compared to current methods, the SIM-GC/MS assay avoids the potential for conversion of Met to MetSO during sample preparation, requires less sample preparation time, has lower variability, and uses mass spectrometry for sensitive and specific analyte detection.

Activation of MAPK by modified low-density lipoproteins in vascular smooth muscle cells

A high concentration of circulating low-density lipoproteins (LDL) is a major risk factor for atherosclerosis. Native LDL and LDL modified by glycation and/or oxidation are increased in diabetic individuals. LDL directly stimulate vascular smooth muscle cell (VSMC) proliferation; however, the mechanisms remain undefined. The extracellular signal-regulated kinase (ERK) pathway mediates changes in cell function and growth. Therefore, we examined the cellular effects of native and modified LDL on ERK phosphorylation in VSMC. Addition of native, mildly modified (oxidized, glycated, glycoxidized) and highly modified (highly oxidized, highly glycoxidized) LDL at 25 microg/ml to rat VSMC for 5 min induced a fivefold increase in ERK phosphorylation. To elucidate the signal transduction pathway by which LDL phosphorylate ERK, we examined the roles of the Ca(2+)/calmodulin pathway, protein kinase C (PKC), src kinase, and mitogen-activated protein kinase kinase (MEK). Treatment of VSMC with the intracellular Ca(2+) chelator EGTA-AM (50 micromol/l) significantly increased ERK phosphorylation induced by native and mildly modified LDL, whereas chelation of extracellular Ca(2+) by EGTA (3 mmol/l) significantly reduced LDL-induced ERK phosphorylation. The calmodulin inhibitor N-(6-aminohexyl)-1-naphthalenesulfonamide (40 micromol/l) significantly decreased ERK phosphorylation induced by all types of LDL. Downregulation of PKC with phorbol myristate acetate (5 micromol/l) markedly reduced LDL-induced ERK phosphorylation. Pretreatment of VSMC with a cell-permeable MEK inhibitor (PD-98059, 40 micromol/l) significantly decreased ERK phosphorylation in response to native and modified LDL. These findings indicate that native and mildly and highly modified LDL utilize similar signaling pathways to phosphorylate ERK and implicate a role for Ca(2+)/calmodulin, PKC, and MEK. These results suggest a potential link between modified LDL, vascular function, and the development of atherosclerosis in diabetes.

Effect of collagen turnover on the accumulation of advanced glycation end products

Collagen molecules in articular cartilage have an exceptionally long lifetime, which makes them susceptible to the accumulation of advanced glycation end products (AGEs). In fact, in comparison to other collagen-rich tissues, articular cartilage contains relatively high amounts of the AGE pentosidine. To test the hypothesis that this higher AGE accumulation is primarily the result of the slow turnover of cartilage collagen, AGE levels in cartilage and skin collagen were compared with the degree of racemization of aspartic acid (% d-Asp, a measure of the residence time of a protein). AGE (N(epsilon)-(carboxymethyl)lysine, N(epsilon)-(carboxyethyl)lysine, and pentosidine) and % d-Asp concentrations increased linearly with age in both cartilage and skin collagen (p < 0.0001). The rate of increase in AGEs was greater in cartilage collagen than in skin collagen (p < 0.0001). % d-Asp was also higher in cartilage collagen than in skin collagen (p < 0.0001), indicating that cartilage collagen has a longer residence time in the tissue, and thus a slower turnover, than skin collagen. In both types of collagen, AGE concentrations increased linearly with % d-Asp (p < 0.0005). Interestingly, the slopes of the curves of AGEs versus % d-Asp, i.e. the rates of accumulation of AGEs corrected for turnover, were identical for cartilage and skin collagen. The present study thus provides the first experimental evidence that protein turnover is a major determinant in AGE accumulation in different collagen types. From the age-related increases in % d-Asp the half-life of cartilage collagen was calculated to be 117 years and that of skin collagen 15 years, thereby providing the first reasonable estimates of the half-lives of these collagens.

Native and modified LDL activate extracellular signal-regulated kinases in mesangial cells

Glycation and/or oxidation of LDL may promote diabetic nephropathy. The mitogen-activated protein kinase (MAPK) cascade, which includes extracellular signal-regulated protein kinases (ERKs), modulates cell function. Therefore, we examined the effects of LDL on ERK phosphorylation in cultured rat mesangial cells. In cells exposed to 100 microg/ml native LDL or LDL modified by glycation, and/or mild or marked (copper-mediated) oxidation, ERK activation peaked at 5 min. Five minutes of exposure to 10-100 microg/ml native or modified LDL produced a concentration-dependent (up to sevenfold) increase in ERK activity. Also, 10 microg/ml native LDL and mildly modified LDL (glycated and/or mildly oxidized) produced significantly greater ERK activation than that induced by copper-oxidized LDL +/- glycation (P < 0.05). Pretreatment of cells with Src kinase and MAPK kinase inhibitors blocked ERK activation by 50-80% (P < 0.05). Native and mildly modified LDL, which are recognized by the native LDL receptor, induced a transient spike of intracellular calcium. Copper-oxidized (+/- glycation) LDL, recognized by the scavenger receptor, induced a sustained rise in intracellular calcium. The intracellular calcium chelator (EGTA/AM) further increased ERK activation by native and mildly modified LDL (P < 0.05). These findings demonstrate that native and modified LDL activate ERKs 1 and 2, an early mitogenic signal, in mesangial cells and provide evidence for a potential link between modified LDL and the development of glomerular injury in diabetes.

Genome-wide characterization of the Zap1p zinc-responsive regulon in yeast

The Zap1p transcription factor senses cellular zinc status and increases expression of its target genes in response to zinc deficiency. Previously known Zap1p-regulated genes encode the Zrt1p, Zrt2p, and Zrt3p zinc transporter genes and Zap1p itself. To allow the characterization of additional genes in yeast important for zinc homeostasis, a systematic study of gene expression on the genome-wide scale was used to identify other Zap1p target genes. Using a combination of DNA microarrays and a computer-assisted analysis of shared motifs in the promoters of similarly regulated genes, we identified 46 genes that are potentially regulated by Zap1p. Zap1p-regulated expression of seven of these newly identified target genes was confirmed independently by using lacZ reporter fusions, suggesting that many of the remaining candidate genes are also Zap1p targets. Our studies demonstrate the efficacy of this combined approach to define the regulon of a specific eukaryotic transcription factor.

X-ray crystallographic and analytical ultracentrifugation analyses of truncated and full-length yeast copper chaperones for SOD (LYS7): a dimer-dimer model of LYS7-SOD association and copper delivery

Copper-zinc superoxide dismutase (CuZnSOD) acquires its catalytic copper ion through interaction with another polypeptide termed the copper chaperone for SOD. Here, we combine X-ray crystallographic and analytical ultracentrifugation methods to characterize rigorously both truncated and full-length forms of apo-LYS7, the yeast copper chaperone for SOD. The 1.55 A crystal structure of LYS7 domain 2 alone (L7D2) was determined by multiple-isomorphous replacement (MIR) methods. The monomeric structure reveals an eight-stranded Greek key beta-barrel similar to that found in yeast CuZnSOD, but it is substantially elongated at one end where the loop regions of the beta-barrel come together to bind a calcium ion. In agreement with the crystal structure, sedimentation velocity experiments indicate that L7D2 is monomeric in solution under all conditions and concentrations that were tested. In contrast, sedimentation velocity and sedimentation equilibrium experiments show that full-length apo-LYS7 exists in a monomer-dimer equilibrium under nonreducing conditions. This equilibrium is shifted toward the dimer by approximately 1 order of magnitude in the presence of phosphate anion. Although the basis for the specificity of the LYS7-SOD interaction as well as the exact mechanism of copper insertion into SOD is unknown, it has been suggested that a monomer of LYS7 and a monomer of SOD may associate to form a heterodimer via L7D2. The data presented here, however, taken together with previously published crystallographic and analytical gel filtration data on full-length LYS7, suggest an alternative model wherein a dimer of LYS7 interacts with a dimer of yeast CuZnSOD. The advantages of the dimer-dimer model over the heterodimer model are enumerated.

The metal binding properties of the zinc site of yeast copper-zinc superoxide dismutase: implications for amyotrophic lateral sclerosis

We have investigated factors that influence the properties of the zinc binding site in yeast copper-zinc superoxide dismutase (CuZnSOD). The properties of yeast CuZnSOD are essentially invariant from pH 5 to pH 9. However, below this pH range there is a change in the nature of the zinc binding site which can be interpreted as either (1) a change in metal binding affinity from strong to weak, (2) the expulsion of the metal bound at this site, or (3) a transition from a normal distorted tetrahedral ligand orientation to a more symmetric arrangement of ligands. This change is strongly reminiscent of a similar pH-induced transition seen for the bovine protein and, based on the data presented herein, is proposed to be a property that is conserved among CuZnSODs. The transition demonstrated for the yeast protein is not only sensitive to the pH of the buffering solution but also to the occupancy and redox status of the adjacent copper binding site. Furthermore, we have investigated the effect of single site mutations on the pH- and redox-sensitivity of Co2+ binding at the zinc site. Each of the mutants H46R, H48Q, H63A, H63E, H80C, G85R, and D83H is capable of binding Co2+ to a zinc site with a distorted tetrahedral geometry similar to that of wild-type. However, they do so only if Cu+ is bound at the copper site or if the pH in raised to near physiological levels, indicating that the change at the zinc binding site seen in the wild-type is conserved in the mutants, albeit with an altered pKa. The mutants H71C and D83A did not bind Co2+ in a wild-type-like fashion under any of the conditions tested. This study reveals that the zinc binding site is exquisitely sensitive to changes in the protein environment. Since three of the mutant yeast proteins investigated here contain mutations analogous to those that cause ALS (amyotrophic lateral sclerosis) in humans, this finding implicates improper metal binding as a mechanism by which CuZnSOD mutants exert their toxic gain of function.

Aminoguanidine and the effects of modified LDL on cultured retinal capillary cells

PURPOSE

Compared with normal low density lipoprotein (N-LDL), LDL minimally modified in vitro by glycation, minimal oxidation, or glycoxidation (G-, MO-, GO-LDL) decreases survival of cultured retinal capillary endothelial cells and pericytes. Similar modifications occurring in vivo in diabetes may contribute to retinopathy. The goal of this study was to determine whether low concentrations of aminoguanidine might prevent cytotoxic modification of LDL and/or protect retinal capillary cells from previously modified LDL.

METHODS

Minimal in vitro modification of LDL (3 days, 37 degrees C) was achieved with glucose (0, 50 mM), under antioxidant conditions (for N-LDL, G-LDL), or under mild oxidant conditions (for MO-, GO-LDL) in the presence/absence of aminoguanidine (0, 1, 10, 100 microM). Glucose and aminoguanidine were then removed by dialysis. Confluent bovine retinal capillary endothelial cells (n = 13) and pericytes (n = 14) were exposed to LDL (100 mg/l) for 3 days, with and without aminoguanidine (100 microM) in media. Cell counts were determined by hemocytometer.

RESULTS

A decrease in cell counts after exposure to modified compared with N-LDL was confirmed (P < 0.001) but was significantly mitigated if LDL had been modified in the presence of aminoguanidine (P < 0.001). Aminoguanidine was as effective at 1 microM as at the higher concentrations. Aminoguanidine (100 microM) present in culture media conferred no additional protection, and showed slight evidence of toxicity. Aminoguanidine present during LDL modification had no effect on measured glycation or oxidation products, or on LDL oxidizability.

CONCLUSIONS

Very low concentrations of aminoguanidine mitigate toxicity of LDL exposed to stresses that simulate the diabetic environment. This action may contribute to the beneficial effects of aminoguanidine observed in experimental diabetic retinopathy.

Pre-enrichment of modified low density lipoproteins with alpha-tocopherol mitigates adverse effects on cultured retinal capillary cells

PURPOSE

We determined whether pre-enrichment of low density lipoproteins (LDL) with alpha-tocopherol mitigates their adverse effects, following in vitro glycation, oxidation or glycoxidation, towards cultured bovine retinal capillary endothelial cells (RCEC) and pericytes.

METHODS

LDL, while still in plasma obtained and pooled from non-diabetic humans, was supplemented in vitro with alpha-tocopherol. It was then isolated and modified in vitro by glycation, minimal oxidation, and glycoxidation. Bovine RCEC and pericytes were exposed to LDL (100mg protein/ ml) for three days. Cell count was determined by cell counting, supernatant levels of plasminogen activator inhibitor-1 (PAI-1) and endothelin-1 (ET-1) by ELISA, and nitrite levels by spectroscopic colorimetric assay.

RESULTS

While pre-enrichment of LDL with alpha-tocopherol did not reduce the measured extent of lipoprotein modification, it abolished the reduction in cell count observed with glycated, oxidized and glycoxidized LDL v. normal LDL. Pre-enrichment of LDL with alpha-tocopherol also reduced RCEC supernatant PAI-1 and ET-1 (corrected for cell counts) and increased RCEC and pericyte-associated supernatant nitrite levels: such effects of alpha-tocopherol may inhibit clot formation and favor vasodilatation.

CONCLUSIONS

Enrichment of LDL with alpha-tocopherol abolishes adverse effects of glycated, mildly oxidized, and glycoxidized LDL on cultured retinal cell count, and mitigates adverse effects on modulators of fibrinolysis and vascular tone. Direct evidence is required before Vitamin E supplementation is recommended for people with diabetes.

Quantification of N-(glucitol)ethanolamine and N-(carboxymethyl)serine: two products of nonenzymatic modification of aminophospholipids formed in vivo

Chemical, nonenzymatic modification of protein and lipids by reducing sugars, such as glucose, is thought to contribute to age-related deterioration in tissue protein and cellular membranes and to the pathogenesis of diabetic complications. This report describes the synthesis and quantification of N-(glucitol)ethanolamine (GE) and N-(carboxymethyl)serine (CMS), two products of nonenzymatic modification of aminophospholipids. GE is the product of reduction and hydrolysis of glycated phosphatidylethanolamine (PE), while CMS is formed through reaction of phosphatidylserine (PS) with products of oxidation of either carbohydrate (glycoxidation) or lipids (lipoxidation). Gas chromatography/mass spectrometry procedures for quantification of the N,O-acetyl methyl ester derivatives of the modified head groups were developed. GE and CMS were quantified in samples of PE and PS, respectively, following incubation with glucose in vitro; CMS formation was dependent on the presence of oxygen during the incubation. Both GE and CMS were detected and quantified in lipid extracts of human red blood cell membranes. The content of GE, but not CMS, was increased in the lipids from diabetic compared to nondiabetic subjects. Measurement of these modified lipids should prove useful for assessing the role of carbonyl-amine reactions of aminophospholipids in aging and age-related diseases.

The role of computed tomography in the diagnosis of arterial gas embolism in fatal diving accidents in Tasmania

Four cases of fatal diving accidents in Tasmania are presented, highlighting the role of CT in the investigation of diving fatalities. The CT technique allows rapid diagnosis when arterial gas embolism (AGE) is suspected. The traditional method of investigation, underwater autopsy, is a difficult procedure that requires specialized training in which the subtle diagnosis of AGE may be completely missed. Facilities for performing underwater autopsies are normally available only in tertiary referral centres, and therefore the diagnosis of AGE may be missed due to lack of facilities. The use of CT in the diagnosis of AGE in divers was first utilized in the early 1980s but has still not become widely adopted in forensic practice. This radiological technique has the advantage of being sensitive, quick, reliable, readily available and provides a permanent record. For hospitals that do not have a resident forensic pathologist, a CT scan can be easily performed and interpreted to eliminate the possibility of AGE. There are a number of pitfalls in the diagnosis of AGE with CT, particularly intravascular gas production following postmortem fermentation and off-gassing. Awareness of these pitfalls will help the radiologist in making a correct diagnosis of AGE.

The transoceanic air evacuation of unstable angina patients

BACKGROUND

The United States Air Force (USAF) air evacuation system in the Western Pacific frequently transports unstable angina patients on fixed wing aircraft over long distances to reach definitive cardiologic and cardiothoracic capabilities. This study begins to answer the question: Does the transfer of unstable angina (i.e., crescendo angina or rest angina) patients over long distances adversely affect the overall outcome of such patients?

METHODS

A case series study was conducted by obtaining a list of urgent and priority unstable angina patients from the Pacific theater from January 1992 through December 1996. Each of these patients' inpatient records were reviewed for cardiac catheterization (cath) result, ejection fraction (EF), previous cardiac history, angioplasty (PTCA) procedures, coronary artery bypass graft (CABG) surgery, and whether a patient had congestive heart failure (CHF), myocardial infarction (MI), death or other complications on this admission.

RESULTS

Of the 59 records reviewed, 61% (36/59) had coronary artery disease (CAD) of at least one vessel greater than 90% occlusion, 31% (18/59) had PTCA, 24% (14/59) had a CABG, 5% (3/59) had CHF, 3% (2/59) had an MI, 24% had some type of a complication, and 1.7% (1) died on this admission.

CONCLUSION

Patients with significant CAD seem to tolerate air transport well with relatively few complications considering the overall morbidity and mortality associated with the diagnosis of unstable angina.

The "push-pull effect" and G-induced loss of consciousness accidents in the U.S. Air Force

BACKGROUND

A recent Canadian Forces CF-18 Hornet aircraft accident has focused interest on the push-pull effect (PPE). PPE has not previously been identified in U.S. Air Force (USAF) G-Induced Loss of Consciousness (G-LOC) Accidents. The presence of maneuvers known to cause the push-pull effect (PPEMs) that lead to G-LOC accidents suggests that PPE is operationally significant and is a potential cause of G-LOC accidents.

METHODS

USAF accident reports where G-LOC was found to be causal were reviewed for indications of a PPEM immediately prior to the G-LOC. Terminology in the narratives was used to indicate a PPEM in the accident sequences.

RESULTS

In 3 of 24 mishaps, the presence of a PPEM was highly probable, while another 4 mishaps were found to have a probable association with PPEMs. The probable presence of PPEMs represents a significant percentage (12.5-29%) of USAF G-LOC accidents.

CONCLUSION

USAF G-LOC accident reports contained descriptions that indicated the presence of PPEMs in accident sequences. This finding suggests that the PPE is an operationally significant source of risk for accidents in USAF high-performance aircraft.

Frequency of the "push-pull effect" in U.S. Air Force fighter operations

BACKGROUND

Recent investigation into the push-pull effect (PPE), the reduction of +Gz tolerance when preceded by less than +1 Gz, has focused on centrifuge studies to demonstrate the presence of adverse cardiovascular responses. Maneuvers found to cause the Push-Pull Effect (PPEM) have not been studied previously in U.S. Air Force (USAF) fighter aircraft. The frequency of and extent to which PPEMs are performed in fighter aircraft are unknown.

METHODS

Head-up display (HUD) videotapes from F-15 and F-16 air combat training missions were reviewed for the presence of PPEMs. The frequency of engagements containing PPEMs and the magnitude of the Gz profiles were noted.

RESULTS

PPEMs were found in 11 to 67%, of engagements reviewed, depending on the nature of the training mission, with an overall average of 32%. The PPEMs that were observed contained segments of less than +1 Gz, ranging on average from 0.0 to 0.5 Gz for an average of 3.5 to 5 s duration.

CONCLUSIONS

PPEMs are present in air combat training missions performed by today's USAF fighter aircraft and represent an operationally significant source of risk for accidents. These findings support continued research into the physiologic response to PPE and the development of countermeasures.

The dark side of dioxygen biochemistry

The cellular biochemistry of dioxygen is Janus-faced. The good side includes numerous enzyme-catalyzed reactions of dioxygen that occur in respiration and normal metabolism, while the dark side encompasses deleterious reactions of species derived from dioxygen that lead to damage of cellular components. These reactive oxygen species have historically been perceived almost exclusively as agents of the dark side, but it has recently become clear that they play beneficial roles as well.

East meets West: a comparison of eastern block/western aeromedical practices

Under the auspices of the European Command (EUCOM) Military-to-Military Exchange Program, the authors participated in 13 trips to visit aeromedical facilities of nine Eastern European nations (Albania, Belarus, Bulgaria, Czech Republic, Hungary, Lithuania, Poland, Romania, and Slovakia). In addition, eight of these Eastern European nations visited United States Air Force (USAF) aeromedical facilities. This article highlights the similarities and differences noted between the USAF and Eastern Europe in the practice of aerospace medicine. Flight surgeons from both Eastern Europe and the USAF address issues such as physiologic stresses of flight (acceleration, hypoxia, etc.) and lifestyle stresses (rest, diet, alcohol, cigarettes, etc.). Eastern European Flight Surgeons do not regularly fly. The Eastern European approach to medical standards and screening for aviation applicants is much stricter and more comprehensive than ours. Several of the nations visited had active research programs at their central aeromedical institute emphasizing aircrew selection and retention standards. With the exception of the Czech Republic, Eastern European nations did not routinely grant waivers for chronic medical conditions such as hypertension in aircrew. Soviet-built aircraft had many unique features such as an outside-in attitude indicator and an auto-recovery system.

Age-dependent increase in ortho-tyrosine and methionine sulfoxide in human skin collagen is not accelerated in diabetes. Evidence against a generalized increase in oxidative stress in diabetes

The glycoxidation products Nepsilon-(carboxymethyl)lysine and pentosidine increase in skin collagen with age and at an accelerated rate in diabetes. Their age-adjusted concentrations in skin collagen are correlated with the severity of diabetic complications. To determine the relative roles of increased glycation and/or oxidation in the accelerated formation of glycoxidation products in diabetes, we measured levels of amino acid oxidation products, distinct from glycoxidative modifications of amino acids, as independent indicators of oxidative stress and damage to collagen in aging and diabetes. We show that ortho-tyrosine and methionine sulfoxide are formed in concert with Nepsilon-(carboxymethyl)lysine and pentosidine during glycoxidation of collagen in vitro, and that they also increase with age in human skin collagen. The age-adjusted levels of these oxidized amino acids in collagen was the same in diabetic and nondiabetic subjects, arguing that diabetes per se does not cause an increase in oxidative stress or damage to extracellular matrix proteins. These results provide evidence for an age-dependent increase in oxidative damage to collagen and support previous conclusions that the increase in glycoxidation products in skin collagen in diabetes can be explained by the increase in glycemia alone, without invoking a generalized, diabetes-dependent increase in oxidative stress.

Carboxymethylethanolamine, a biomarker of phospholipid modification during the maillard reaction in vivo

Nepsilon-(Carboxymethyl)lysine (CML) is a stable chemical modification of proteins formed from both carbohydrates and lipids during autoxidation reactions. We hypothesized that carboxymethyl lipids such as (carboxymethyl)phosphatidylethanolamine (carboxymethyl-PE) would also be formed in these reactions, and we therefore developed a gas chromatography-mass spectrometry assay for quantification of carboxymethylethanolamine (CME) following hydrolysis of phospholipids. In vitro, CME was formed during glycation of dioleoyl-PE under air and from linoleoylpalmitoyl-PE, but not from dioleoyl-PE, in the absence of glucose. In vivo, CME was detected in lipid extracts of red blood cell membranes, approximately 0.14 mmol of CME/mol of ethanolamine, from control and diabetic subjects, (n = 22, p >> 0.5). Levels of CML in erythrocyte membrane proteins were approximately 0.2 mmol/mol of lysine for both control and diabetic subjects (p >> 0.5). For this group of diabetic subjects there was no indication of increased oxidative modification of either lipid or protein components of red cell membranes. CME was also detected in fasting urine at 2-3 nmol/mg of creatinine in control and diabetic subjects (p = 0.085). CME inhibited detection of advanced glycation end product (AGE)-modified protein in a competitive enzyme-linked immunosorbent assay using an anti-AGE antibody previously shown to recognize CML, suggesting that carboxymethyl-PE may be a component of AGE lipids detected in AGE low density lipoprotein. Measurement of levels of CME in blood, tissues, and urine should be useful for assessing oxidative damage to membrane lipids during aging and in disease.

Lipoprotein glycation and its metabolic consequences

Glycation of lipoproteins is implicated in the development of the macro- and microvascular complications of diabetes, atherosclerosis in general, and other disease processes including aging. Enhanced glycation may have direct effects, and may also amplify the effects of oxidative stress on lipoproteins. Most studies have examined the effects of glycation of LDL, particularly with respect to its atherogenicity. Other lipoproteins are more difficult to study because their several apolipoproteins, being of varying age, are not uniformly exposed to glucose. Inhibition of the combined stresses of glycation and oxidation towards lipoproteins may have beneficial effects on health.

Assessment of the anti-G straining maneuver (AGSM) skill performance and reinforcement program

Initial high-G centrifuge training of USAF fast jet pilots was instituted in 1985. Also, since the mid-1980's, pilot awareness of G-induced loss of consciousness (G-LOC) has been enhanced by briefings, videotapes, and safety articles. Aircraft accidents caused by an improperly performed anti-G straining maneuver (AGSM), however, continue to occur. Deficiencies in the AGSM of pilots in flight have not been systematically studied. A test program to reinforce the proper performance of the AGSM in flight was initiated in the United States Air Forces Europe (USAFE) in 1993. Head-up display videotapes (HUD tapes) were recorded during flight and critiqued during debrief by flight leads for AGSM technique and continuity. Questionnaires were completed by F-16, F-15C, and F-15E pilots assigned to USAFE: 78 surveys were completed out of 110 distributed (71%). There were 57 pilots (73%) who reported one or more problems with their AGSM: 33 noted that the timing of their breathing was too quick (< 2 s cycle), 11 that their breathing was too slow (> 4 s), 9 that inhalation was too long, 18 occasionally did not "get the jump on the Gs," and 34 frequently or occasionally talked during +Gz exposures. Of the 105 reported deficiencies, 67 (64%) were mostly or completely corrected: 30/33 (91%) if the timing of breathing was too quick, 8/11 (73%) if too slow, 5/9 (56%) if inhalation too long, 12/18 (67%) "jump on the Gs," and 12/34 (35%) if they talked. This program was most successful in remediating timing problems with the AGSM.

Quantification of malondialdehyde and 4-hydroxynonenal adducts to lysine residues in native and oxidized human low-density lipoprotein

Malondialdehyde (MDA) and 4-hydroxynonenal (HNE) are major end-products of oxidation of polyunsaturated fatty acids, and are frequently measured as indicators of lipid peroxidation and oxidative stress in vivo. MDA forms Schiff-base adducts with lysine residues and cross-links proteins in vitro; HNE also reacts with lysines, primarily via a Michael addition reaction. We have developed methods using NaBH4 reduction to stabilize these adducts to conditions used for acid hydrolysis of protein, and have prepared reduced forms of lysine-MDA [3-(N epsilon-lysino)propan-1-ol (LM)], the lysine-MDA-lysine iminopropene cross-link [1,3-di(N epsilon-lysino)propane (LML)] and lysine-HNE [3-(N epsilon-lysino)-4-hydroxynonan-l-ol (LHNE)]. Gas chromatography/MS assays have been developed for quantification of the reduced compounds in protein. RNase incubated with MDA or HNE was used as a model for quantification of the adducts by gas chromatography/MS. There was excellent agreement between measurement of MDA bound to RNase as LM and LML, and as thiobarbituric acid-MDA adducts measured by HPLC; these adducts accounted for 70-80% of total lysine loss during the reaction with MDA. LM and LML (0.002-0.12 mmol/ mol of lysine) were also found in freshly isolated low-density lipoprotein (LDL) from healthy subjects. LHNE was measured in RNase treated with HNE, but was not detectable in native LDL. LM, LML and LHNE increased in concert with the formation of conjugated dienes during the copper-catalysed oxidation of LDL, but accounted for modification of < 1% of lysine residues in oxidized LDL. These results are the first report of direct chemical measurement of MDA and HNE adducts to lysine residues in LDL. LM, LML and LHNE should be useful as biomarkers of lipid peroxidative modification of protein and of oxidative stress in vitro and in vivo.

Hospitals and managed care: catching up with the networks

Although the growth of managed care is having a significant impact on hospitals, organizational response to managed care remains fragmented. We conducted a survey of 83 hospitals nationwide that indicated that most hospitals now have at least one person devoted to managed care initiatives. These individuals, however, often spend most of their time on current issues, such as contracting with managed care organizations and physician relations. Concerns for the future, such as network development and marketing, although important, receive less immediate attention form these individuals. Hospital managed care executives must take a more proactive role in long range managed care planning by collaborating with managed care organizations and pharmaceutical companies.

Glycation, oxidation, and lipoxidation in the development of the complications of diabetes: a carbonyl stress hypothesis

Modifications of extant plasma proteins, structural proteins, and other macromolecules are enhanced in diabetes because of increased glycation (secondary to increased glucose concentrations) and perhaps because of increased oxidative stress. Increased glycation is present from the time of onset of diabetes, but the relation between diabetes and oxidative stress is less clear: increased oxidative stress may occur later in the course of disease, as vascular damage becomes established, or it may be a feature of uncomplicated diabetes. The combined effects of protein modification by glycation and oxidation may contribute to the development of accelerated atherosclerosis in diabetes and to the development of microvascular complications. Thus, even if not increased by diabetes, variations in oxidative stress may modulate the consequences of hyperglycemia in individual diabetic patients. In this review, the close interaction between glycation and oxidative processes is discussed, and the theme is developed that the most significant modifications of proteins are the result of interactions with reactive carbonyl groups. While glucose itself contains a carbonyl group that is involved in the initial glycation reaction, the most important and reactive carbonyls are formed by free radical-oxidation reactions damaging either carbohydrates (including glucose itself) or lipids. The resulting carbonyl-containing intermediate products then modify proteins, yielding "glycoxidation" and "lipoxidation" products, respectively. This common pathway for glucose and lipid-mediated stress, which may contribute to diabetic complications, is the basis for the carbonyl stress hypothesis for the development of diabetic complications.

Brain cancer, flying, and socioeconomic status: a nested case-control study of USAF aircrew

We compared the brain cancer risk of male United States Air Force (USAF) aircrew (37 cases) with nonflying Air Force personnel (193 cases) between 1970 and 1989.

METHODS

Incident brain cancer cases for both aviators and nonflying USAF personnel were obtained from USAF hospitalization records. Age, race, and calendar time matched controls were randomly selected for each case from the remaining USAF cohort. We estimated brain cancer risks using conditional logistic regression models.

RESULTS

Initially, we observed a statistically significant brain cancer excess for USAF aircrew compared to nonflying USAF personnel (Odds Ratio [OR] = 1.77, 95% Confidence interval [95% CI] 1.17-2.68). However, following adjustment for senior military rank, a socioeconomic status indicator, the USAF aircrew brain cancer risk was markedly reduced (OR = 1.22, 95% CI 0.76-1.95), demonstrating that much of the previously observed USAF aircrew brain cancer risk was attributable to factors other than flying.

CONCLUSION

The results of this investigation indicate that flying is not an important brain cancer risk factor, at least for USAF aircrew. The positive relationships observed in other studies between commercial aircrew and brain cancer risk may have been confounded by social class differentials.

Mutations in copper-zinc superoxide dismutase that cause amyotrophic lateral sclerosis alter the zinc binding site and the redox behavior of the protein

A series of mutant human and yeast copper-zinc superoxide dismutases has been prepared, with mutations corresponding to those found in familial amyotrophic lateral sclerosis (ALS; also known as Lou Gehrig's disease). These proteins have been characterized with respect to their metal-binding characteristics and their redox reactivities. Replacement of Zn2+ ion in the zinc sites of several of these proteins with either Cu2+ or Co2+ gave metal-substituted derivatives with spectroscopic properties different from those of the analogous derivative of the wild-type proteins, indicating that the geometries of binding of these metal ions to the zinc site were affected by the mutations. Several of the ALS-associated mutant copper-zinc superoxide dismutases were also found to be reduced by ascorbate at significantly greater rate than the wild-type proteins. We conclude that similar alterations in the properties of the zinc binding site can be caused by mutations scattered throughout the protein structure. This finding may help to explain what is perhaps the most perplexing question in copper-zinc superoxide dismutase-associated familial ALS-i.e., how such a diverse set of mutations can result in the same gain of function that causes the disease.

Neuroendocrine carcinoma of the larynx

Neuroendocrine carcinomas (NEC) of the larynx are rare. The key to diagnosis is therefore an increased awareness of such lesions amongst otolaryngologists and pathologists. A precise histological diagnosis is crucial, as the management is different for each NEC sub-type. Advances in immunohistochemistry have been a great help in this respect. We report a typical case of large cell NEC (atypical carcinoid) and highlight the clinical pointers to the histological diagnosis.

The advanced glycation end product, Nepsilon-(carboxymethyl)lysine, is a product of both lipid peroxidation and glycoxidation reactions

Nepsilon-(Carboxymethyl)lysine (CML) is an advanced glycation end product formed on protein by combined nonenzymatic glycation and oxidation (glycoxidation) reactions. We now report that CML is also formed during metal-catalyzed oxidation of polyunsaturated fatty acids in the presence of protein. During copper-catalyzed oxidation in vitro, the CML content of low density lipoprotein increased in concert with conjugated dienes but was independent of the presence of the Amadori compound, fructoselysine, on the protein. CML was also formed in a time-dependent manner in RNase incubated under aerobic conditions in phosphate buffer containing arachidonate or linoleate; only trace amounts of CML were formed from oleate. After 6 days of incubation the yield of CML in RNase from arachidonate was approximately 0.7 mmol/mol lysine compared with only 0.03 mmol/mol lysine for protein incubated under the same conditions with glucose. Glyoxal, a known precursor of CML, was also formed during incubation of RNase with arachidonate. These results suggest that lipid peroxidation, as well as glycoxidation, may be an important source of CML in tissue proteins in vivo and that CML may be a general marker of oxidative stress and long term damage to protein in aging, atherosclerosis, and diabetes.

Cancer incidence in United States Air Force aircrew, 1975-89

We compared the cancer incidence of male United States Air Force (USAF) aircrew (342 cancers, 532,980.97 man-years) with non-flying Air Force officers (827 cancers, 1,084,370.08 man-years) between 1975-89.

METHODS

Incident cancer cases for both aviators and non-flying officers were obtained from USAF hospitalization records. Age-adjusted standardized incidence ratios (SIR's) were calculated for aircrew using data from the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) program. Aviator age-adjusted cancer rate ratios were also obtained using non-flying officers as an internal comparison group.

RESULTS

We observed statistically significant excesses of aircrew cancers for all sites, testis, and urinary bladder. All other aviator cancer classifications were not significantly different from the comparison cohort; most notably, cancers of the colon and rectum, skin (both malignant melanoma and non-epithelial), brain and nervous system, Hodgkin's Disease and leukemias.

CONCLUSION

Previous studies of commercial pilots that demonstrated excesses of these cancers may have been biased by the use of external comparison groups. We used an internal comparison population to reduce selection bias, information bias and confounding. From these data we detected notable excess aircrew cancer risk for cancers of the testis, urinary bladder, and all sites combined.

Lipoxidation products as biomarkers of oxidative damage to proteins during lipid peroxidation reactions

Oxidative stress is implicated in the pathogenesis of numerous disease processes including diabetes mellitus, atherosclerosis, ischaemia reperfusion injury and rheumatoid arthritis. Chemical modification of amino acids in protein during lipid peroxidation results in the formation of lipoxidation products which may serve as indicators of oxidative stress in vivo. The focus of the studies described here was initially to identify chemical modifications of protein derived exclusively from lipids in order to assess the role of lipid peroxidative damage in the pathogenesis of disease. Malondialdehye (MDA) and 4-hydroxynonenal (HNE) are well characterized oxidation products of polyunsaturated fatty acids on low-density lipoprotein (LDL) and adducts of these compounds have been detected by immunological means in atherosclerotic plaque. Thus, we first developed gas chromatography-mass spectrometry assays for the Schiff base adduct of MDA to lysine, the lysine-MDA-lysine diimine cross-link and the Michael addition product of HNE to lysine. Using these assays, we showed that the concentrations of all three compounds increased significantly in LDL during metal-catalysed oxidation in vitro. The concentration of the advanced glycation end-product N epsilon-(carboxymethyl)lysine (CML) also increased during LDL oxidation, while that of its putative carbohydrate precursor the Amadori compound N epsilon-(1-deoxyfructose-1-yl)lysine did not change, demonstrating that CML is a marker of both glycoxidation and lipoxidation reactions. These results suggest that MDA and HNE adducts to lysine residues should serve as biomarkers of lipid modification resulting from lipid peroxidation reactions, while CML may serve as a biomarker of general oxidative stress resulting from both carbohydrate and lipid oxidation reactions.

External ear canal cholesteatoma. Case report

External ear canal cholesteatoma is a rare condition in otologic practice. A case in a 43-year-old woman is presented in which despite the extensive nature of the lesion, minimal symptoms and absence of signs delayed diagnosis. The cause of the lesion and its treatment are discussed.